Methods of making electric resistance heating mats

ABSTRACT

The method of making an electric heating mat including disposing laterally spaced portions of electric resistance wire on a support, disposing a plastic extrusion head over the support and extruding a strand of plastic downwardly toward the wire portions, and relatively moving the support and extrusion head to lay the downwardly extruded strand cross-wise of and over the wire portions, the strand adhering to the portions at the places of crossing to form a dielectric strand connection between the wire portions.

United States Patent McFarlane [54] METHODS OF MAKING ELECTRIC RESISTANCE HEATING MATS [72] Inventor: William McFarlane, Murfreesboro, Tenn. [73] Assignee: Emerson Electric Co.

[22] Filed: June 29, 1970 211 Appl. No.: 60,165

Related US. Application Data [62] Division Of SCI/N0, 662,796, Aug. 23, 1967.

[52] U.S.Cl ..29/6ll,2l9/2l3,219/549,

338/212 [51] Int. Cl. ..H06b 3/00 [58] Field ofSearch ..29/61 1; 219/545, 549, 528,

[5 6] References Cited UNITED STATES PATENTS 3,191,005 6/1965 Cox... ..2l9/549X [15] 3,659,338 1 May 2,1972

3,193,664 7/1965 Beery ..338/210 X 3,330,035 7/1967 Pradenas ..29/61 1 3,584,198 6/1971 Kazuo et al. ..338/212 X FOREIGN PATENTS OR APPLICATIONS 506,803 10/1954 Canada ..338/212 Primary Examiner-John F. Campbell Assistant Examiner-Victor A. DiPalma Attorney-Williams and Kreski [57] ABSTRACT The method of making an electric heating mat including disposing laterally spaced portions of electric resistance wire on a support, disposing a plastic extrusion head over the support and extruding a strand of plastic downwardly toward the wire portions, and relatively moving the support and extrusion head to lay the downwardly extruded strand cross-wise of and over the wire portions, the strand adhering to the portions at the places of crossing to form a dielectric strand connection between the wire portions.

9 Claims, 13 Drawing Figures PATENTEUMAY 21912 3,659,338 SHEET 10F 5 INVENTOR. WILLIAM MCFARLANE' PATENTEDMAY 2M2 3,659,338

SHEET 2 UF 5 INVENTOR A T OR/V15 X5 WlLLlAM Mc FARLANE V PATENTEDMAY 2 I972 SHEET 3 UF 5 PIG-7 INVENTOR. WlLLIAM Mc FARLANE I PATENTEDMAY 21912 I INVENTOR. WILLIAM MCFARLANE v PATENTEDMAY 2 i972 INVENTOR. W\LL|AM MCFARLANE METHODS or MAKING ELECTRIC RESISTANCE HEATING MATS This is a division of application Ser. No. 662,796, filed Aug. 23, 1967, for Methods of and Apparatus for Making Electric Resistance Heating Mats.

PREAMBLE Electric resistance heating mats of the type which can be embedded in concrete for snow melting, or embedded or otherwise attached to walls, ceilings orfloors for heating a room, have long been known and used. Such mats have even been fonned by disposing electric resistance wire portions in a predetermined pattern and retaining such wire portions in position with each other by means of thermoplastic strands extending across the wire portions and adhered thereto.

Prior art methods and apparatus for making electric heating mats of the type hereinabove described, however, were slow and costly whereas the present invention provides methods and apparatus which drastically increases speed of manufacture of electric heating mats while greatly reducing manufacturing costs thereof. These and other advantages will readily become apparent from a study of the following description and from the appended drawings.

. OUTLINE OF DRAWINGS In the drawings accompanying this specification and forming a part of this application there is shown, for purpose of illustration, an embodiment which the invention may assume, and in these drawings:

FIG. 1 is agenerally diagrammatic, top plan view of apparatus embodying the present invention,

FIG. 2 is aside elevational view of the apparatus seen in FIG. 1,

FIG. 3 is an enlarged plan view of an electric resistance heater mat made in accordance with the present invention,

FIG. 4 is an enlarged, sectional view generally corresponding to the line 44 ofFIG. 3,

FIG. 5 is a diagrammatic plan view showing the pattern in which a single strand of thermoplastic material is deposited on a moving conveyor by a reciprocating extrusion head,

FIG. 6 is a view like FIG. 5 but showing the pattern in which two strands are deposited when the extrusion head apertures from which respective strands issue are spaced from each other in a direction from side-to-side of the direction of conveyor movement,

FIG. 7 is a view like FIG. 6 but showing the pattern formed when respective head apertures are spaced from each other in the direction of conveyor movement,

- FIG. 8 is a view like FIG. 6 but showing the pattern formed when respective apertures are spaced from each other both in the direction of conveyor movement and in a direction from side-to-side of conveyor movement,

FIG. 9 is a view similar to FIGS. 58 but showing the pattern formed when the extrusion head is formed with six apertures, arranged in two rows of three each, from which thermoplastic strands simultaneously issue,

FIG. 10 is a view similar to FIG. 3 but showing the pattern in which the strands will be deposited when the center pair of extrusion head apertures seen in FIG. 9 are omitted,

FIG. 11 is a view similar to FIG. 3 but with resistor wires arranged in a different pattern and with but a single thermoplastic strand extruded thereonto,

FIG. 12 is a view similar to FIG. 3 but of a heatermat formed by a non-reciprocating extrusion head, and

FIG. 13 is a view similar to FIG. 3 but of a double width heater mat formed of two resistor wires electrically interconnected in series relation.

DETAILED DESCRIPTION With reference to FIGS. 1 and 2, apparatus for the manufacture of electric heating mats of the type illustrated in FIG. 3 is generally diagrammatically shown. Such apparatus preferably comprises a conveyor 10 driven by a motor and having an upper reach adapted to receive an electric resistance heating wire 11 arranged in a predetermined pattern in which certain wire portions are disposed in spaced, side-byside relation. In FIG. 1, the wire 11 is shown arranged in a sinuous pattern; however, other wire patterns may be employed as will later appear. Although not shown, the conveyor may carry pins or the like for temporarily maintaining the wire in the described pattern as it is moved by the conveyor from left to right in the position of parts illustrated.

Spaced from the left, or entry end of conveyor 10, is extruding apparatus 12 having a head 13 spaced slightly above the upper reach of the conveyor. Head 13 of the extruder is adapted to be reciprocated in a direction from side-to-side of the conveyor, as by means of a suitably controlled fluid cylinder 14, for a purpose to appear. Suitable apertures, of a number and arrangement later to be disclosed, are formed in the underside of head 13 and a suitable thermoplastic material, such as low density polyethylene, is adapted to be heated to a plastic state and extruded as thin strands through the head apertures for deposit upon the underlying, upper reach of the conveyor and over the wire pattern disposed thereon.

To facilitate understanding of the function of the extrusion head in depositing strands of thermoplastic material on the wire pattern, attention is directed to FIGS. 5 through 9. In each of such FIGS., the upper reach of conveyor 10a will be assumed to be moving at a predetermined constant rate in a direction from left to right while the extrusion head 13a will be assumed to be reciprocated a predetermined amount in a direction from side-to-side of the conveyor at a constant rate and with a slight dwell intermediate its travel reversals.

Turning first to FIG. 5 and assuming the extrusion head 13a be provided with a single aperture through which thermoplastic material issues, a strand Sa will be deposited on the moving conveyor in the pattern shown if the head is reciprocated the amount indicated at X. Note that the elongated, angularly disposed strand portions are formed during traversing movement of the extrusion head while the short, interconnecting strand portions which are aligned with the direction of conveyor movement are formed while the extrusion head is momentarilyimmobilized between each reversal of direction of its traversing movement.

In the event the extrusion head is provided with two apertures from which thermoplastic material issues and assuming such apertures are spaced from each other the amount shown at X in the direction of head movement and in alignment therewith (see FIG. 6), a pair of strands Sa will be deposited in spaced, side-by-side relation in precise registry with each other. Note that in this instance, corresponding portions of respective strands are in parallel relation.

In FIG. 7, the extrusion head is still provided with two apertures; however, in this instance, the apertures are in alignment with the direction of conveyor movement and are spaced from each other an amount equal to one half the longitudinal spacing between adjoining, corresponding peaks in the strand as deposited on the conveyor. For clarity of disclosure, the strand deposited by the aperture on the right side of the head is shown by solid line while the strand deposited by the aperture on the left of the head is shown by broken line. Note that with this arrangement of apertures, strands are deposited, one superimposed upon the other, but with the peaks formed by respective strands offset from each other longitudinally of the conveyor. Since the strands are quite plastic when first deposited on the conveyor, they will adhere to each other at their places of intersection.

Turning to FIG. 8, if the head is still provided with two apertures but with such apertures spaced from each other both longitudinally of conveyor movement and transversely thereof; that is, an aperture spacing which is a combination of that shown in FIG. 6 and that shown in FIG. 7, the illustrated diamond-shaped configuration of thermoplastic strands will be deposited. Here again, the strand deposited by the aperture on the right side of the head is shown by solid line while the apertures 15, 15.1; 16, 16.1, and 17, 17.1. The apertures of each aperture pair are aligned with but spaced from each other in the direction of conveyor movement, the aperture pairs are spaced from each other in a direction transverse to conveyor movement an amount equal to the amount of reciprocation of head l3, and the apertures 15, 16 and 17 are aligned with each other in the direction of head movement as are the apertures 15.1, 16.1 and 17.1. Upon movement of the conveyor 10 and reciprocation of the extrusion head 13 as 'shown and described, the full line strands 3 will be deposited upon the moving conveyor from the head apertures 15, 16 and 17 while the broken line strands will be deposited by the head apertures 15.1, 16.1 and 17.1. As previously mentioned, since the strands are in a heated, very plastic state when deposited on the conveyor, they will adhere to each other at their places of intersection and, when such strands cool and solidify, the illustrated mesh structure, having considerable strength,'will be provided. From the foregoing, it will be evident that if the strand pattern seen in FIG. 9 is deposited upon and adhered to a resistor wire, an integrated structure will be provided when the strands cool and solidify.

Returning to FIG. 1, a suitable electric resistor wire 11 will be placed upon the entry orleft end of theconveyor 10 in, for example, the sinuous pattern'shown. The resistor wire 10 will preferably be of the insulated type having a coating 11.1 (see FIG. 4) of the same thermoplastic material as that extruded from the head 13. v Disposed above the upper reach of the conveyor 10 ahead of the extrusion head 13 there is shown a radiant heater 18 (see also FIG. 2) adapted to heat the underlying resistor wire sufficiently that its insulating coating willbecome soft enough to insure its adherence with the strands deposited by the extrusion head. While the use of a radiant heater has been shown, it will be understood that other expedients may be employed to insure adherence between the heater wire and the extruded strands of thermoplastic material. As an example, electric current might be passed through the resistor wire to raise the tem-' perature of its coating the requisite amount.

As the heated sinuous resistor wire 11 is carried by the conveyor l beneath the reciprocating extrusion head 13, the thermoplastic strands seen in FIG. 9 will be deposited thereon and adhered thereto. To facilitate cooling and solidification of the plastic strands and the wire coating, a fan unit'or the like 19 may direct a cooling flow of air upon the upper reach of the conveyor and on the heater mat thus formed. From the foregoing, it will be evident that the heater mat may be formed in any practical length desired and then cut transversely to provide a mat of the length desired. Thereafter, as seen in FIG. 3, suitable lead wires 20 may be connected to respective ends of the resistor wire to provide for connection of the latter into an electrical power circuit.

The embodiment of the invention seen in FIG. is similar to that seen in FIG. 3; accordingly, similar parts are identified by the same reference characters but with the suffix b appended. Bearing in mind that the thermoplastic strands S seen in FIG. 3 are deposited by an extrusion head having the three pair of apertures seen in FIG. 9, the strands Sb are deposited by an extrusion head in which the central pair of apertures 16, 16.1 of FIG. 9 are omitted to thus omit from the mat the center row of diamonds previously formed by the strands deposited by such apertures.

As heretofore disclosed, the heating mat has been formed by moving a single resistor wire disposed in a sinuous pattern beneath a transversely reciprocating extrusion head having a plurality of apertures from which thermoplastic strands issue for deposit upon the resistor as it passes beneath the head. However, heating mats having other configurations may also be made.

With reference to FIG. 11 wherein corresponding parts are identified by the same reference characters as before but with the suffix 0 added, the resistor wire pattern is formed of a plurality of wires 11c in spaced, side-by-side relation. Such wires will extend longitudinally of the conveyor previously described and will be carried beneath the extrusion head as before. In this embodiment, however, the extrusion head will be provided with but a single aperture to extrude a single strand Sc of thermoplastic material on to the resistor wire pattern. The heater mat thus formed will be completed by securing lead wires 20c across the resistor wires thus connecting the latter together in parallel circuits.

In the embodiment seen in FIG. 12 wherein corresponding parts are identified by the same reference characters as before but with the suffix d" added, the resistor wire 11d has the same form as the resistor wire 11 in FIG. 3 and is moved beneath the extrusion head as previously described. In this embodiment, however, the extrusion head will be provided with five apertures in spaced-apart, transversely aligned relation to extrude respective strands Sd of thermoplastic material on to the resistor wire pattern as it moves beneath the head. In this embodiment, the head is held stationary so that the strands Sd are deposited on the wire pattern in spaced, parallel relation. Ultimately, as before, the mat will be cut transversely to the desired length and lead wires 20d will be connected to respective resistor wire ends.

The embodiment of the invention seen in FIG. 13 is similar to that seen in FIG. 3 and corresponding parts are identified by the same reference characters but with the suffix e" added. In this embodiment, a pair of resistor wires are each arranged on the conveyor as previously described but in side-by-side relation. In the manufacture of such a mat, of course, the conveyor will be wide enough to accommodate the two resistor wires. The thermoplastic strands Se will be deposited on the resistor wire pattern by a reciprocating extrusion head as described with respect to FIG. 3; however, since the wire pattern of FIG. 13 is substantially twice as wide as that previously described, the extrusion head will be provided with six pairs of apertures rather than the three pairs earlier described.

With the mat thus formed out to the desired length, adjoining resistor wire ends at one end may be joined by a connecting wire 21 while the leads 20e may be secured to the adjoining resistor wires at the other mat end. Thus, the resistor wires 11e are in series relation and the leads 20e areconveniently disposed in side-by-side relation.

While it presently appears that satisfactory adherence between the resistor wire and the thermoplastic strands will be effectuated merely by preheating the resistor wire as heretofore described, it may in some instances be desirable to apply. additional heat after the strands are deposited upon the resistor wire. Accordingly and with reference to FIG. 2, this may easily be accomplished by providing a radiant heater 118 (similar to radiant heater 18) which heats the resistor wire and the overlying thermoplastic strands as they are carried beyond the extrusion head by the underlying conveyor.

In view of the foregoing it will be apparent to those skilled in the art that I have accomplished at least the principal object of my invention and it will also be apparent to those skilled in the art that the embodiments herein described may be variously changed and modified, without departing from the spirit of the invention, and that the invention is capable of uses and has advantages not herein specifically described; hence it will be appreciated that the herein disclosed embodiments are illustrative only and that my invention is not limited thereto.

I claim:

1. The method of making an electric heating mat having an electric resistance heating wire and a strand of flexible, thermoplastic material adhered together, which comprises forming electric resistor wire in a pattern wherein certain wire portions are in laterally spaced relation with each other,

disposing said patterned wire beneath an extrusion head,

and extruding a strand of thermoplastic material from said head on to said wire pattern while efiecting relative movement therebetween to cause said strand to cross said wire portions.

2. The method of claim 1 which further comprises heating at least one of said heating mat components sufiiciently to effect adherence therebetween.

3. The method of claim 2 which further comprises heating said wire prior to extrusion of said strand of material thereon sufficiently to effect adherence therebetween.

4. The method of claim 2 which further comprises heating the assembled wire and strand sufficiently to effect adherence therebetween.

5. The method of claim 1 which further comprises disposing said wire in the pattern aforesaid on a conveyor,

operating said conveyor to move said wire pattern in a path beneath said extrusion head,

and reciprocating said extrusion head in a direction from side-to-side of the path of travel of said wire pattern.

6. The method of claim 5 which further comprises simultaneously extruding a pair of strands from said head on to said wire pattern from places offset from each other in the direction of the path of travel of said wire pattern.

7. The method of claim 5 which further comprises simultaneously extruding a pair of strands from said head on to said wire pattern from places offset from each other in a direction from side-to-side of the path of travel of said wire pattern.

8. The method of claim 5 which further comprises simultaneously extruding a plurality of strands from said head on to said wire pattern from places in part ofi'set in the direction of the path of travel of said wire pattern and in part offset in a direction from side-to-side of said travel path.

9. The method of claim 7 which further comprises reciprocating said head an amount at least equal to the amount of ofiset aforesaid to cause overlapping of respective strands with each other. 

1. The method of making an electric heating mat having an electric resistance heating wire and a strand of flexible, thermoplastic material adhered together, which comprises forming electric resistor wire in a pattern wherein certain wire portions are in laterally spaced relation with each other, disposing said patterned wire beneath an extrusion head, and extruding a strand of thermoplastic material from said head on to said wire pattern while effecting relative movement therebetween to cause said strand to cross said wire portions.
 2. The method of claim 1 which further comprises heating at least one of said heating mat components sufficiently to effect adherence therebetween.
 3. The method of claim 2 which further comprises heating said wire prior to extrusion of said strand of material thereon sufficiently to effect adherence therebetween.
 4. The method of claim 2 which further comprises heating the assembled wire and strand sufficiently to effect adherence therebetween.
 5. The method of claim 1 which further comprises disposing said wire in the pattern aforesaid on a conveyor, operating said conveyor to move said wire pattern in a path beneath said extrusion head, and reciprocating said extrusion head in a direction from side-to-side of the path of travel of said wire pattern.
 6. The method of claim 5 which further comprises simultaneously extruding a pair of strands from said head on to said wire pattern from places offset from each other in the direction of the path of travel of said wire pattern.
 7. The method of claim 5 which further comprises simultaneously extruding a pair of strands from said head on to said wire pattern from places offset from each other in a direction from side-to-side of the path of travel of said wire pattern.
 8. The method of claim 5 which further comprises simultaneously extruding a plurality of strands from said head on to said wire pattern from places in part offset in the direction of the path of travel of said wire pattern and in part offset in a direction from side-to-side of said travel path.
 9. The method of claim 7 which further comprises reciprocating said head an amount at least equal to the amount of offset aforesaid to cause overlapping of respective strands with each other. 